Science Overview I: (Polarized) e-p Collisions Nuclear Science Goals: How do we understand the visible matter in our universe in terms of the fundamental quarks and gluons of QCD?  Explore the structure of the nucleon (it’s what we are made of) Rolf Ent (JLab) for the EIC Collaboration EICAC Meeting SURA Headquarters, Washington D.C. February 16, 2009

EIC science has evolved from new insights and technical accomplishments over the last decade ~1996 development of Generalized Parton Distributions ~1999 high-power energy recovery linac technology ~2000 universal properties of strongly interacting glue ~2000 emergence of transverse-spin phenomenon ~2001 world’s first high energy polarized proton collider ~2003 tantalizing hints of saturation ~2006 electron cooling for high-energy beams Still many ongoing developments: constraints on gluon polarization, 1 st tests of crab cavities, development of semi-inclusive DIS framework at NLO, 2 nd round of deep exclusive measurements, Lattice QCD progress, etc., etc.

NSAC 2007 Long Range Plan “An Electron-Ion Collider (EIC) with polarized beams has been embraced by the U.S. nuclear science community as embodying the vision for reaching the next QCD frontier. EIC would provide unique capabilities for the study of QCD well beyond those available at existing facilities worldwide and complementary to those planned for the next generation of accelerators in Europe and Asia. In support of this new direction: We recommend the allocation of resources to develop accelerator and detector technology necessary to lay the foundation for a polarized Electron Ion Collider. The EIC would explore the new QCD frontier of strong color fields in nuclei and precisely image the gluons in the proton.”

Precisely image the quarks and gluons in the nucleon - How do the gluons and quarks contribute to the spin structure of the nucleon? - What is the spatial distribution of the gluons and quarks in the nucleon? - How do hadronic final-states form in QCD? Nuclear Science Goals: How do we understand the visible matter in our universe in terms of the fundamental quarks and gluons of QCD? (Polarized) e-p Collisions Science Goal: Transformational or incremental?

Nuclear Science Goals: How do we understand the visible matter in our universe in terms of the fundamental quarks and gluons of QCD? A large scale view of the universe: Astronomy picture of the day, Feb. 11, Orion’s Belt. A small scale view of the universe: Cartoon of a nucleon… - What is the spatial distribution of the gluons and quarks in the nucleon? - How do hadronic final-states form in QCD? But, some recent progress in transverse imaging and QCD visualizations from Lattice QCD. E = Mc 2 The root of Modern Physics: But, we only know how this actually works in cartoon form …

Nuclear Science Goals: How do we understand the visible matter in our universe in terms of the fundamental quarks and gluons of QCD? - How do the gluons and quarks contribute to the spin structure of the nucleon?

The Spin of the Proton Nobel Prize, 1943: "for his contribution to the development of the molecular ray method and his discovery of the magnetic moment of the proton"  p = 2.5 nuclear magnetons, ± 10% (1933) Otto Stern Proton spins are used to image the structure and function of the human body using the technique of magnetic resonance imaging. Paul C. Lauterbur Sir Peter Mansfield Nobel Prize, 2003: "for their discoveries concerning magnetic resonance imaging"

But where does the spin of the proton originate? (let alone other hadrons…) The Standard Model tells us that spin arises from the spins and orbital angular momentum of the quarks and gluons: ½ = ½  +  G + L q + L g Experiment:  ≈ 0.3 Gluons contribute to ≈ half of the mass and momentum of the proton, but… … recent results indicate that their contribution to the proton spin is small:  G < 0.1? … and recent LQCD tells us that L u + L d is small?? (but…)

Where does the spin of the proton originate? Input from DIS, SIDIS, pp (RHIC) and Global Fits… De Florian, Sassot, Stratmann and Vogelsang, Phys. Rev. Lett. 101, (2008)  G < 0.1? (constrained in narrow region of x only)

Where does the spin of the proton originate? … and input from Lattice QCD on GPD moments (also from deep exclusive scattering) LHPC Collaboration, Phys. Rev. D77, (2008) L u and L d separately quite substantial (~0.15), but cancel (disconnected diagrams not yet included)

Where does the spin of the proton originate? Generalized Parton Distributions provide access to total quark contribution to proton angular momentum in (deep) exclusive processes: e + N  e’ + N + X ½ = J q + J g = ½  + L q + J g H(x, ,t), E(x, ,t),.. “Generalized Parton Distributions” Accessible through deep exclusive reactions (and Lattice QCD) Quark angular momentum (Ji’s sum rule) X. Ji, Phy.Rev.Lett.78,610(1997) k k'k' ** q q'q'  pp'p' e

What’s the use of GPDs? 2. Describe correlations of quarks/gluons 3. Allows access to quark angular momentum (in model-dependent way) 1. Allows for a unified description of form factors and parton distributions gives transverse spatial distribution of quark (parton) with momentum fraction x Fourier transform in momentum transfer x < 0.1x ~ 0.3x ~ Allows for Transverse Imaging

Explore the structure of the nucleon Parton distribution functions Longitudinal and transverse spin distribution functions Generalized parton distributions Unintegrated parton distribution functions Examples of EIC science simulations Will emphasize proton, but neutron results equally important: spectator tagging in D(e,e’p)X ideal for collider plans to use both polarized 2 H and 3 He beams

Luminosity of 1x10 33 cm -2 sec -1 One day  50 events/pb Supports Precision Experiments Lower value of x scales as s -1 DIS Limit for Q 2 > 1 GeV 2 implies x down to 1.0 times Significant results for 200 events/pb for inclusive scattering If Q 2 > 10 GeV 2 required for Deep Exclusive Processes can reach x down to 1.0 times Typical cross sections factor ,000 smaller than inclusive scattering Significant results for 20, ,000 events/pb  high luminosity essential Luminosity Considerations for EIC eRHIC (20 GeV e - ) eRHIC, ELIC (W 2 > 4) x Q 2 (GeV 2 ) W 2 <4 eRHIC: x = 10 Q 2 = 1 ELIC : x = 10 Q 2 = 1 12 GeV: x = 4.5x10 Q 2 = 1 Include low-Q 2 region eRHIC-staged: s = 2000  x = 5x10 2 =1 ELIC-staged: s = 600  x = 1.7x10 2 =1

CTEQ Example at Scale Q 2 = 10 GeV 2 Gluon distributions as large as down quarks at high-x.

Longitudinal Structure Function F L Experimentally can be determined directly IF VARIABLE ENERGIES! Highly sensitive to effects of gluon + 12-GeV data EIC alone F L at EIC: Measuring the Glue Directly How to measure Gluon distribution G(x,Q 2 ): Scaling violation in F 2 :  F 2 /  lnQ 2 F L ~  s G(x,Q 2 ) inelastic vector meson production (e.g. J/  ) diffractive vector meson production ~ [G(x,Q 2 )] 2

World Data on F 2 p World Data on g 1 p  50% of momentum carried by gluons  30% of proton spin carried by quark spin The dream is to produce a similar plot for x  g(x) vs x

World Data on F 2 p World Data on g 1 p  50% of momentum carried by gluons An EIC makes it possible!

The Gluon Contribution to the Proton Spin at small x Superb sensitivity to  g at small x! (Antje Bruell, Abhay Deshpande)

Projected data on  g/g with an EIC, via  + p  D 0 + X K - +  + assuming vertex separation of 100  m. Access to  g/g is also possible from the g 1 p measurements through the QCD evolution, and from di-jet measurements. RHIC-Spin The Gluon Contribution to the Proton Spin Advantage: measurements directly at fixed Q 2 ~ 10 GeV 2 scale! Uncertainties in x  g smaller than 0.01 Measure 90% of  G Q 2 = 10 GeV 2 )  g/g

5 on 50 EIC projected data x Bj Flavor EIC Lower x ~ 1/s 5 on 50  s = x Bj 100 days at (Ed Kinney, Joe Seele)  quark polarization  q(x)  first 5-flavor separation  u > 0  d < 0 10 on 250  s = Polarized pdfs also constrained through Electroweak DIS! 10 on 250 EIC projected data x Bj

RHIC-Spin region Precisely image the sea quarks Spin-Flavor Decomposition of the Light Quark Sea | p = … > u u d u u u u d u u d d d Many models predict  u > 0,  d < 0 No competition foreseen!

GPDs and Transverse Imaging Deep exclusive measurements in ep/eA with an EIC: diffractive:transverse gluon imagingJ/ ,  o,  (DVCS) non-diffractive:quark spin/flavor structure , K,  +, … [ or J/ , ,  0 , K,  +, … ] Describe correlation of longitudinal momentum and transverse position of quarks/gluons  Transverse quark/gluon imaging of nucleon (“tomography”)

GPDs and Transverse Gluon Imaging Goal: Transverse gluon imaging of nucleon over wide range of x: < x < 0.1 Requires: - Q 2 ~ GeV 2 to facilitate interpretation - Wide Q 2, W 2 (x) range - Sufficient luminosity to do differential measurements in Q 2, W 2, t Q 2 = 10 GeV 2 projected data Simultaneous data at other Q 2 -values EIC enables gluon imaging! (Andrzej Sandacz)

- New territory for collider! - Much more demanding in luminosity (see example) - Physics closely related to JLab 6/12 GeV - quark spin/flavor separations - nucleon/meson structure Γ dσ/dt (  b/GeV 2 ) Extend to Quark Imaging: Non-Diffractive Channels Pushes for lower and more symmetric energies (to obtain sufficient  M x ) Simulation for charged  + production, assuming 100 days at a luminosity of 10 34, with 5 on 50 GeV (s = 1000) Ch. Weiss: Regge model T. Horn: π + empirical parameterization 10<Q 2 <15 15<Q 2 <20 35<Q 2 <40 (Tanja Horn, Antje Bruell, Christian Weiss)

(polarized) e-p at medium energies Exclusive processes and GPDs – Deeply-Virtual Meson Production: spin/flavor/spatial quark structure (Q 2 ~ 10 GeV 2 ) – DVCS: helicity GPDs, spatial quark and gluon imaging Charm as direct probe of gluons – J/ ψ, exclusive : spatial distribution of gluons – D Λ c, open charm (including quasi-real D 0 photoproduction for Δ G) Semi-inclusive DIS – Flavor decomposition: q ↔ q, u ↔ d, strangeness s, s – TMDs: spin-orbit interactions from azimuthal asymmetries, p T dependence – Target fragmentation and fracture functions Inclusive DIS – Δ G and Δ q+ Δ q from global fits (+ RHIC-spin, COMPASS, JLab 12 GeV) – Neutron structure from spectator tagging in D(e,e’p)X -- -

The Future of Fragmentation un-integrated: current fragmentation target fragmentation FF from vacuum   Can we understand the physical mechanism of fragmentation and how do we calculate it quantitatively?

Detector design Alternate detector: Emphasize low-x, low-Q 2 diffractive physics (“HERA-III design”, MPI-Munchen) Si tracking stations EM calorimeter e p/A Main detector: learn from ZEUS (and H1) But:low-field option around central tracker better particle identification forward-angle detectors auxiliary detectors for exclusive events auxiliary detectors for normalization Main detector: Emphasize high-luminosity full physics program Hadronic calorimeter

Present Main Detector cartoon

Detector R&D (Detector R&D is same for full EIC and staged options) General R&D items: 1.Particle Id. Detectors a.Study alternate (cheaper) materials than quartz for DIRC, allowing for momenta > 3 GeV b.Develop a TRD that allows for e/h separation at ~1 GeV 2.Photon Detection a.Develop cost-effective photon detection replacing PMTs like big area SiPMTs -Compact and work in magnetic field w.o. shielding -Perfect single photon resolution (for DIRC/RICH) 3.Small angle particle tracking a.Radiation hard (diamond?) electron detectors b.High-efficiency neutron detectors 4.High precision electron and ion beam polarimetry specific R&D related to 500 MHz operation (more detailed recipe next slide)

Detector R&D (Detector R&D is same for full EIC and staged options) specific R&D related to 500 MHz operation: Detector Signal Capture and Trigger System 1.High-Speed Flash ADCs a.JLAB design operates at 4 ns sampling (250MHz) which is adequate for many detector signal shapes b.Commercial ADC chips are available at 2 ns (500MHz) and 1 ns (1GHz) sampling c.Engineering design will be needed to solve cooling issues and board layout challenges d.Continue R&D efforts with latest FPGA technology  500 MHz clocking exists now on some devices e.Continue R&D efforts to use industry standards: (VXS, or new VPX) for extremely high speed serial transmission for Level 1 trigger decisions and global timing synchronization 2.Multi-crate DAQ with L1 trigger rates > 150KHz a.JLAB prototype multi-crate system achieves 165KHz at 80MB/s b.Explore the use of high speed serial links as data transfer paths rather than VME backplane method c.Continue R&D of Crate Trigger Processor algorithms and Global Trigger hardware designs 3.EIC Readout/DAQ Electronics (in int’l collab.) a.R&D for new vertex detector readout chips: Most designs are for much longer bunch crossing time b.FPGA design/simulation and firmware code sharing c.Detector data rate simulation including trigger rate studies to improve trigger system design

Summary The last decade or so has seen tremendous progress in our understanding of the partonic sub-structure of nucleons and nuclei based upon: The US nuclear physics flagship facilities: RHIC and CEBAF The surprises found at HERA (H1, ZEUS, HERMES) The development of a theory framework allowing for a revolution in our understanding of the inside of hadrons … QCD Factorization, Lattice QCD, Saturation This has led to new frontiers of nuclear science: - the possibility to truly explore the nucleon - a new QCD regime of strong color fields The EIC presents a unique opportunity to maintain US and BNL&JLab leadership in high energy nuclear physics and precision QCD physics

Energy Considerations for EIC FacilityenergiesCM energy [GeV] (Peak) Luminosity x Q 2 = 1 x Q 2 = GeVFixed target 53x x x10 -1 eRHIC10 x x x x10 -3 eRHIC (staged) 4 x x x x10 -3 ELIC10 X x x x10 -3 ELIC (staged) 5 x x x x10 -2 Q 2 = 1 gives DIS range in x, Q 2 = 10 gives lever arm in Q 2

Proposed EIC recommendation for the Galveston meeting A high luminosity Electron-Ion Collider (EIC) is the highest priority of the QCD community for new construction after the JLab 12 GeV and RHIC II luminosity upgrades. EIC will address compelling physics questions essential for understanding the fundamental structure of matter: - Explore the new QCD frontier: strong color fields in nuclei; - Precisely image the sea-quarks and gluons to determine the spin, flavor and spatial structure of the nucleon. This goal requires that R&D resources be allocated for expeditious development of collider and detector design. Galveston estimate: $4M/year for accelerator R&D, $2M/year for detector R&D (Five years each)

The Bjorken Sum Rule Precision QCD test, at present measured at 10-15% level Aim to measure with 1-2% absolute uncertainty with EIC. Severe demand on proton and 3 He or 2 H beam polarimetry (or in-situ calibration reaction). Lattice can give confidence in small-x extrapolations. 1-2% statistical precision at fixed Q 2 needs high luminosity. Could potentially give the best determination of  s ! s = 4200

Projected A(W - ) Assuming xF 3 will be known Parity-Violating g 5 Structure Function To date unmeasured due to lack of high Q 2 polarized e-p possibility. From 2002 White Paper (Contreras et al). Assumptions: 1)Q 2 > 225 GeV 2 2)One month at luminosity of Requires positron beam

New Spin Structure Function: Transversity Nucleon’s transverse spin content  “tensor charge” No transversity of Gluons in Nucleon  “all-valence object” Chiral Odd  only measurable in semi-inclusive DIS  first glimpses from HERMES  COMPASS 1 st results: low x  valence region only?  Future: Flavor decomposition (started by Anselmino et al.) - (in transverse basis)  q(x) ~ Need (high) transverse ion polarization (Naomi Makins, Ralf Seidl)

Vanish like 1/p T (Yuan) Correlation between Transverse Spin and Momentum of Quarks in Unpolarized Target All Projected Data Perturbatively Calculable at Large p T - (Harut Avakian, Antje Bruell)

GPDs and Transverse Gluon Imaging gives transverse size of quark (parton) with longitud. momentum fraction x EIC: 1) x < 0.1: gluons! x < 0.1x ~ 0.3x ~ 0.8 Fourier transform in momentum transfer x ~ )  ~ 0  the “take out” and “put back” gluons act coherently. 2)  ~ 0 x -  x +   d

GPDs and Transverse Gluon Imaging Two-gluon exchange dominant for J/ , ,  production at large energies  sensitive to gluon distribution squared! LO factorization ~ color dipole picture  access to gluon spatial distribution in nuclei: see eA! Measurements at DESY of diffractive channels ( J/ , , ,  ) confirmed the applicability of QCD factorization: t-slopes universal at high Q 2 flavor relations  :  Unique access to transverse gluon imaging at EIC! Fit with d  /dt = e -Bt

GPDs and Transverse Gluon Imaging k k'k' ** q q'q'  pp'p' e A Major new direction in Nuclear Science aimed at the 3-D mapping of the quark structure of the nucleon. Simplest process: Deep-Virtual Compton Scattering Simultaneous measurements over large range in x, Q 2, t at EIC! At small x (large W):  ~ G(x,Q 2 ) 2

Deeply Virtual Exclusive Processes - Kinematics Coverage of the 12 GeV Upgrade JLab Upgrade Upgraded JLab has complementary & unique capabilities unique to JLab overlap with other experiments High x only reachable with high luminosity H1, ZEUS

The Future of Fragmentation p h x TMD  D Current Fragmentation h q Can we understand the physical mechanism of fragmentation and how do we calculate it quantitatively? Target Fragmentation p M h  d  h ~  q f q (x)  D f h (z) d  h ~  q  M h/p q (x,z) QCD Evolution Correlate at EIC

Gluons dominate QCD QCD is the fundamental theory that describes structure and interactions in nuclear matter. Without gluons there are no protons, no neutrons, and no atomic nuclei Gluons dominate the structure of the QCD vacuum Facts: –The essential features of QCD (e.g. asymptotic freedom, chiral symmetry breaking, and color confinement) are all driven by the gluons! –Unique aspect of QCD is the self interaction of the gluons –98% of mass of the visible universe arises from glue –Half of the nucleon momentum is carried by gluons

What are the phases of strongly interacting matter and what roles do they play in the cosmos? What is the internal landscape of the nucleons? What does QCD predict for the properties of strongly interacting matter? What governs the transition of quarks and gluons into pions and nucleons? What is the role of gluons and gluon self-interactions in nucleons and nuclei? What determines the key features of QCD, and what is their relation to the quantum nature of gravity and spacetime? NSAC LRP December 2007: Overarching QCD Questions